Concerns about the health and materials degradation impacts of ultraviolet (UV) radiation are being raised with increasing frequency. UV radiation from the sun can cause skin cancers, eye problems, and can degrades light-sensitive artifacts. Traditional chemical sunscreens act primarily by binding to skin protein and absorbing UVB (280-320 nm) photons. The majority of these sunscreens are based on para-aminobenzoic acid, cinnamates such as methoxycinnamate, and various salicylates. Although these substances tend to absorb strongly in the UVB range, many of these substances do not absorb sunlight strongly in the UVA range (320-400 nm). Many commercial preparations are weak UVB/UVA absorbers, including benzophenones, dibenzoylmethanes, and anthraline derivatives, which have a limited UVA absorption as well. Octocrylene is a weak but stable UVB absorber used to protect other agents from degrading. Avobenzone (Parsol-1789) is a benzophenone with fair UVA protection, but it degrades readily and tends to cause irritation when applied to the skin. All of these organic sunscreens can cause allergic or irritant contact dermatitis, photoxic, and photoallergic reactions and no single organic agent gives complete protection from UVA and UVB radiation.
In addition to organic agents, inorganic agents, often referred to as sunblocks, act as barriers by reflecting or scattering radiation. These physical blockers include metal oxide compounds such as iron, zinc, titanium and bismuth. Iron oxide pigments are incorporated in many personal care products, and provide protection from not only UV radiation, but visible and IR (infrared) radiation as well. Zinc Oxide (ZnO) and Titanium Dioxide (TiO2) are highly reflective white powders. In the personal care product industry, bulk inorganic UV absorbers such as ZnO and TiO2 have been used for many years to protect people from the effects of UV radiation. Inorganic UV absorbers have many desirable characteristics such as a long history of topical use, low irritancy, broad spectrum absorption and high photo-stability. Zinc oxide, being inorganic, is photostable and thus as opposed to the majority of organic absorbers, its effectiveness as a UV absorber is not lessened over time with sunlight exposure. However, rather than absorbing UV radiation, ZnO, TiO2 and other inorganic components of personal care products are typically used to scatter light. The scattering of light by these inorganic particles causes a whitening effect on a users skin once applied which leads to poor cosmetic appeal. Thus, the recognized value of ZnO as an acceptable UV skin protector is decreased due to this whitening effect.
An additional problem associated with inorganic components of sunscreen is that they often do not disperse well in many personal care ingredients. Additionally, inorganic absorbers due to their relatively large particle size may lead to aggregation.
There is a need for a UV absorber that does not have the whitening effect typical of inorganic UV absorbers and that are soluble in and may be dispersed evenly in oily skin lotions.